使用Python和树莓派的LED条矩阵进行FFT

Question

我在用Python和一个LED灯带搞事情。这个LED灯带用的是WS2801芯片，可以通过SPI来控制，排列成一个矩阵，像这样：

     ----      ----      ----      ----
140 |    |    |    |    |    |    |    | 15
    |    |    |    |    |    |    |    |
    |    |    |    |    |    |    |    |
    |    |    |    |    |    |    |    |
    |    |    |    |    |    |    |    |
    |    |    |    |    |    |    |    |
    |    |    |    |    |    |    |    |
    |    |    |    |    |    |    |    |
    |    |    |    |    |    |    |    |
    |    |    |    |    |    |    |    |
    |    |    |    |    |    |    |    |
    |    |    |    |    |    |    |    |
    |    |    |    |    |    |    |    |
    |    |    |    |    |    |    |    |
    |    |    |    |    |    |    |    |
155 |    |    |    |    |    |    |    | 0
          ----      ----      ----

每个短横线代表一个LED灯（一个像素）。每列有16个像素，总共有8行。

编号是从右下角开始的。所以最右边的列从0开始，到15结束。中间的四个像素是不会亮的。所以第二右边的列从上到下的编号是20到35。

最左边的列从顶部的140到底部的155。

我想做的是在播放歌曲的时候显示它的频谱。低频的应该在左边的列显示，高频的则在右边的列显示。

我的代码是基于PixelPi的（https://github.com/scottjgibson/PixelPi）。我省略了FFT的部分，因为那不是问题所在。

# Each pixel consumes 3 bytes
PIXEL_SIZE = 3 

# Lots of colors
BLACK = bytearray(b'\x00\x00\x00')
AQUA = bytearray(b'\x00\xff\xff')
AQUAMARINE = bytearray(b'\x7f\xff\xd4')

def filter_pixel(input_pixel, brightness):
    output_pixel = bytearray(PIXEL_SIZE)

    input_pixel[0] = int(brightness * input_pixel[0])
    input_pixel[1] = int(brightness * input_pixel[1])
    input_pixel[2] = int(brightness * input_pixel[2])

    output_pixel[0] = gamma[input_pixel[0]]
    output_pixel[1] = gamma[input_pixel[1]]
    output_pixel[2] = gamma[input_pixel[2]]
    return output_pixel

# Initialize LED strip matrix
height  = 16
base    = [155, 120, 115, 80, 75, 40, 35, 0]
# Do the indexes of this column go from bottom to top?
up      = [False, True, False, True, False, True, False, True]
color   = [NAVY, RED, MAROON, DARKBLUE, DARKCYAN, PALEGREEN, YELLOWGREEN, YELLOW]

# Output matrix, filled with black pixels
empty_output = bytearray(args.num_leds * PIXEL_SIZE + 3)
for led in range(args.num_leds):
    empty_output[led * PIXEL_SIZE:] = filter_pixel(BLACK, 1)

current_color = bytearray(PIXEL_SIZE)
corrected_color = bytearray(PIXEL_SIZE)

while True: # (Actually while song is playing)

    # Returns an array of length 8 with values between 0 and 4095
    matrix = calculate_levels(matrix, weighting, data, CHUNK_SIZE, sample_rate)

    # Copy the matrix with only black pixels. Copying seems to be faster than resetting all not needed pixels to black
    pixel_output[:] = empty_output


    for col in range(len(base)):
        current_color[:] = color[col][:]
            # Do some gamma correction
        corrected_color[:] = filter_pixel(current_color[:], 1)

            # Each column is 16 pixels high. The maximum value of the FFT to be returned for each column is 4095. 4096 / 256 = 16
        lighted_height = round(matrix[col]/float(1 << 8), 2)

        for row in range(max(16, int(lighted_height) + 1)):
            pixel_index = base[col] + row if up[col] == True else base[col] - row
            pixel_index = pixel_index * PIXEL_SIZE

            if (row < int(lighted_height)):
                # Pixel's brightness in 100%
                pixel_output[pixel_index:] = corrected_color[:]
            elif (row <= int(lighted_height) and row + 1 > int(lighted_height)):
                # Pixel's brightness is between 0 and 1
                pixel_output[pixel_index:] = filter_pixel(current_color[:], lighted_height - int(lighted_height))

            #print "[col:", col, ", row:", row, "] : ", pixel_index, "lighted_height:", lighted_height, "int(lighted_height)", int(lighted_height), "lighted:", lighted

            # As I uncomment these two lines, at least all pixels on the other columns are displayed.
            #spidev.write(pixel_output)
            #spidev.flush()

    spidev.write(pixel_output)
    spidev.flush()

问题是这段代码只点亮了最右边的那一列（0到15）。其他的列似乎都是黑的。

当我把spidev.write(pixel_output)和spidev.flush()放在列循环里，这样每列的像素输出都能写入时，其他列的某些灯亮了。但是它们的亮起方式有点随机，而且声音也不再流畅了。

顺便说一下，LED灯带在PixelPi的示例中，比如渐变和追逐效果，都表现得很好。

这可能是WS2801芯片的一些特性我不知道吗？还是我没有正确计算像素输出矩阵？

更新：还有一件奇怪的事：

i = 0
x = 0
while x < 160:
    if i != 0 and i % 16 == 0:
    x = x + 4

    pixel_index = x * PIXEL_SIZE
    pixel_output[pixel_index:] = filter_pixel(WHITE, 1)

    i = i + 1
    x = x + 1

    print "i, x", i, x

    time.sleep(0.1)
    spidev.write(pixel_output)
    spidev.flush()

这段代码本来应该点亮从像素0到最后一个，并在执行16次循环后跳过4个像素。然而，它并没有跳过一个像素，因此在到达最后一个像素之前就停止了。

树莓派 LED矩阵 fft ws2801 spi pixelpi 音频频谱像素控制

使用Python和树莓派的LED条矩阵进行FFT

1 个回答

撰写回答